In recent years, there has been proposed a stereoscopic image display device such as television set capable of displaying stereoscopic images. One known system for displaying stereoscopic images allows the viewer, who wears dedicated glasses for viewing stereoscopic images, to recognize a two-dimensional image as a stereoscopic image. One promising system proposed at present is to allow the viewer, who wears glasses (G) for viewing stereoscopic images, to see images on a liquid crystal display device on which right-eye images and left-eye images, which are parallax images (disparity images), are alternately displayed in a time-series manner (for example, see Patent Literature 1).
In this sort of system making use of a liquid crystal shutter, both of systems using glasses with two polarizing plates and using glasses with a single polarizing plate need a λ/4 plate, in order to improve display performance obtainable when the viewer inclines the head. In particular, this is particularly important for the case where the glasses with a single polarizing plate are used.
The λ/4 plate is necessary also on the viewing side of the stereoscopic image display device, corresponding to the glasses for viewing stereoscopic images. Since the larger the stereoscopic image display device, the larger the effect of stereopsis, so that there is a strong demand for larger display device, and therefore there is a demand for large λ/4 plate suitable for large size display.
On the other hand, for further improvement in contrast of a liquid crystal display device, there has been discussed introduction of a front plate made of glass or acrylic resin on the viewing side of a conventional liquid crystal panel. By providing the front plate, diffused reflection due to irregularities on a surface of a conventional polarizing plate protective film may be reduced, and this ensures high-contrast and edgy expression of color.
The front plate, when bonded to the liquid crystal panel, may degrade the contrast when a void is formed in between, since the external light may cause multiple reflection on the interfaces. It is therefore preferable to provide a sealing layer for bringing the front plate and the liquid crystal panel into close contact while avoiding the void. Among various methods of curing the sealing layer such as heat curing, pressure-sensitive adhesion and so forth, the best choice is a method of UV curing using a UV-curable resin for the sealing layer.
For example, Patent Literature 2 discloses a technique of tightly bonding the liquid crystal panel and the front plate while placing a photo-curable resin in between, by irradiating it by light of 340 nm or longer wavelength, so as to eliminate wavelength components of shorter than 340 nm which may adversely affect the liquid crystal molecule, adhesive and so forth, thereby preventing the liquid crystal panel from being degraded and thus the quality of display is maintained.
The front plate made of glass or acrylic resin is not generally used alone, but is used typically in combination with a resin film having a hard coat layer for scratch prevention and antireflection. Accordingly, taking the productivity into account, a preferable method would be such that a sealing layer which has a UV-curable tacky agent, a front plate composed of glass or acrylic resin, an adhesive layer, and a resin film which has a hard coat layer are stacked in this order on the surface on the viewing side of the liquid crystal panel which has polarizing plates on both sides of the liquid crystal cell, and curing the sealing layer by irradiating it with UV light from the hard coat layer side.
When the front plate is attached to the stereoscopic image display device, it is preferable from the viewpoint of productivity to bond the λ/4 plate to the front plate. In this case, by using the λ/4 plate having a hard coat layer as the resin film, it becomes unnecessary to provide an additional hard coat film or λ/4 plate and successfully reduces the number of components of the stereoscopic image display device, which contributes to slimming of the display device.
Another problem, however, arose in the process of curing the sealing layer by UV irradiation from the hard coat layer side. That is, when irradiation dose of UV is increased aiming at delivering a necessary and sufficient amount of light for curing to the sealing layer, it induces heat load or UV load to the λ/4 plate having the hard coat layer and resulted in wrinkle or deformation between the hard coat layer and the λ/4 plate or peeling of the hard coat layer. In the stereoscopic image display device in need of precise parallax, even a slight wrinkle or deformation can result in lowered luminance and hue change, and crosstalk caused by the viewer's head inclination when viewing stereoscopic (3D) images.